It is recommended that a pond system’s complete volume is turned over at least once every 2 hours. For example, if a pond has a volume of 2000 gallons, a pump capable of pumping a minimum of 1000 gallons per hour would be required. However, most performance data provided by pump manufacturers will relate to performance in an ideal, blanketweed-free environment where restrictive pipe work is not a problem – so take care to read the pump data carefully. The work that a pump has to achieve in pumping water outside the pond, say to a filter and waterfall, will also have serious implications for the choice of the pump.
You want the best pump for your garden pond? see these pumps
Head or flow restrictions?
As soon as a pump has to move water vertically, its flow rate is reduced. The vertical distance between the water’s surface and the delivery height of the pipe is described as the ‘head’ with the greater the head, the lower the pump turnover. For example, if a pond has a volume of 2000 gallons, and requires a turnover of 1000 gallons per hour, if that same pond has a waterfall that is 3 feet high, then a suitable pump would be one that provides a turnover of 1000 gallons per hour (minimum) at 3 feet of head. This will mean choosing a larger pump than you may have first expected.
Furthermore, for a waterfall to look realistic, with the full channel width covered in flowing water, sufficient water must be delivered by the pump to the top. A flow of 500 gallons per hour is usually required for a waterfall 6” wide and if a pump is not able to deliver this flow, then a waterfall will be a rather disappointing trickle rather than a cascading flow.
The advice when choosing a pump is the same when considering the size of a pond or filter: Always be inclined to opt for the largest one possible as it will provide your koi with a superior environment in the long run. A greater flow rate can easily be reduced, but if the pump is too small for the job, you’ll have to buy a new one – an expensive mistake!
What about other pieces of pond equipment – Will they affect pump performance?
Variations in pipework between different systems can have a profound effect on pump performance. This will include in-line items such as UVcs and heaters.
When piping water from a pump to a filter, use as few elbows as possible, tending towards the use of sweeping bends in flexible hose if possible. This will reduce the friction of the water in pipework, maintaining pump performance. Always use the pipe diameter as recommended by the pump’s manufacturer (even if reducing hose-tail adaptors are provided with the pump) as deviating from the ideal diameter will also reduce pump performance.
Should you consider power consumption?
As a pump is likely to be used continuously, the running cost is a significant consideration when pricing up a pump for your particular pond. Power consumption is measured in Watts with a greater figure relating to a power-hungry pump (that is more costly to run). The wattage will not always relate to the overall performance of a pump as efficiencies in design and construction can enable some lower wattage pumps to outperform pumps with larger motors. The difference in running costs over the lengthy lifespan of two different pumps could amount to the price of a new pump.
Will your new pump give you value for money?
Pump running costs must always be taken into account.
For example, for every 100 watts difference between two pumps with the same output, the difference in running cost per year will be:
1 year = 8760 hours @ 100 watts = 876 KWh
1 KWh costs 6p.
Total difference in running costs between two pumps over 1 year:
6p x 876 = £52.56
Over a 5 year life, this will cost £262.80 which might be the cost of a new pump (or a nice koi)
Some pumps may be fitted with foam or perforated plastic pre-filters to prevent impellors from becoming blocked. These can reduce pump performance even when only partially blocked. More recently, pumps that will handle solids up to 10mm have become available on the market which are ideal for traditional weed-free koi ponds. Where a pump is situated in the final pump chamber of a gravity-fed system, then pump blockages should not be a problem.
As a measure of how reliable (and competitive) pond pumps have become, most pumps are now sold with a free extended warranty of anything up to 5 years. With standard maintenance and the use of correct pipework so as not to produce high back pressures, then even these lengthy guarantees should easily be exceeded. Pumps are more likely to be temperamental if they are frequently switched on and off rather than used continuously and problems can also occur with pumps becoming blocked with debris or blanketweed, choking the impellor and leading to a burn-out.
Other desirable features
Many submersible pumps are fitted with additional safety features. Float switches are a safety back-up which prevents pumps from burning out should they run dry. Should the water level within a pump chamber drop, then the change in angle of the float switch will cause the pump to switch off. An additional safety feature found in many pumps is a thermal cut-out which also switches the pump off should it over heat. This will also protect the pump should it run dry.
What’s the best way of finding out all this information?
Once you have calculated the volume of your system, head requirements etc you will have established your pump’s required theoretical output (at that head). You then need to visit a koi or pond specialist that will display a range of different pumps so you can compare the pump performance curves, power consumption and even guarantee. Handle the pump, see how rugged it feels and how easy it will be to plumb into your system. Remember, you should be buying on value (over at least a 3 year period), rather than the ticket price of the pump itself. Mail order or Internet-based retailers may be able to give you the best price, but what service will they offer in the event of a breakdown. Remember that a pump is synonymous with the pond’s heart – and if it fails, a speedy replacement is essential. Again, buy on the value (based on the product and the service) rather than on up-front costs.
Factors that affect pump performance:
1. Blocked inlet / pre-filter
2. Vertical head required to pump
3. Friction losses through pipework (elbows, restrictions etc)
Boxout: Pump Guide – Different types of pump and the jobs they do
Most popular design. Ranges from a small fountain pump to one capable of pumping several thousand gallons of water per hour. Designed to run continuously. Will have varying solids-handling capabilities – depending on the design.
Also a submersible pump, but typically designed for intermittent work (ie cellar pump). May be fitted with a float-switch. Takes water from the very bottom of the pump body.
Pump body must remain dry. Typically found in larger ponds requiring greater turnover and pump pressure. Need to be installed in a dedicated dry chamber or housing. May require priming if situated above the water surface.
Have to hand your own pond’s requirements:
Submersible or External Pump?
Volume (gallons / litres)
If you’re buying a replacement pump, what’s the diameter of your existing pipework?
Facts you need to find out in store when comparing pumps prior to buying:
Turnover at your required head
Reliability / reputation (ie what brand does the retailer use / recommend?)
Maintenance / solids handling issues
Power consumption (Watts) (and how that will affect running costs and overall cost of purchase)
Length and terms of guarantee
Likely support in the event of a pump failure?
Length of cable